An apparatus of the kind described above is disclosed in German Patent 3,615,830.
If highly viscous materials such as certain types of rubber are to be processed in such an apparatus, major problems with the radial sealing of the gear faces occur, this being the reason why such temperature sensitive materials have not been processed in gear-pump-type apparatus thus far.
Axial sealing of the shafts for the gears, however, is relatively unproblematic because of helical return threads.
Sealing the end faces of the gears to the housing in radial direction down to the shaft of the gears constitutes a most difficult problem. It is indispensable for the conveyance of temperature sensitive rubber to avoid the formation of dead corners or dead space in the apparatus because the rubber would be partially vulcanized there, which would contaminate the compound and, thus, render it unusable.